Pregnancy rates in cattle with cryopreserved sexed spermatozoa: effects of laser intensity, staining conditions and catalase

Abstract

The overall aim of this research was to improve fertility of cattle inseminated with sexed spermatozoa by improving sperm sorting procedures. Six field trials were conducted in which 4,264 heifers were inseminated into the uterine body with cryopreserved sexed or unsexed control spermatozoa. Pregnancy or calving rates with doses of 2 x 10(6) sexed spermatozoa ranged from 32 to 51%; these averaged 69% of the pregnancy rates with 20 x 10(6) unsexed, control spermatozoa (range 53 to 79% of controls). Fertility of sexed spermatozoa was especially low on farms where control fertility was low. Accuracy of sexing ranged from 86 to 91%. Laser power of 150 mW for interrogating spermatozoa did not result in lower pregnancy rates (43%) than when power was decreased as much as possible for a particular sorting batch (50 to 130 mW) to still achieve sexing accuracy (38% pregnant). Addition of catalase to fluids containing spermatozoa was beneficial when thawed spermatozoa were incubated in vitro for 2 h but had no effect on pregnancy rates. There also was no effect on pregnancy rates between two concentrations of Hoechst 33342 for staining spermatozoa. Freezing 2 x 10(6) sexed spermatozoa at 20 x 10(6)/ml resulted in a slightly higher rate of pregnancy (P < 0.05) than at 10 x 10(6)/ml. The information obtained in these trials, along with other improvements, notably lowering pressure in the sorting system from 50 to 40 psi, has been used to improve procedures for sexing spermatozoa commercially.